1. Field of the Invention
In general, this invention relates to vibration dampers. More specifically, this invention relates to vibration dampers that include a silica-containing, viscoelastic vibration damping material. The invention further relates to articles that incorporate the vibration dampers as well as a method of vibration damping.
2. Description of the Related Art
Vibration dampers are well known. Vibration dampers typically include a viscoelastic material that is applied to an article that experiences resonant vibrations. The viscoelastic material absorbs and dissipates the vibrational energy, thereby damping the vibrations and reducing any associated noise. Sometimes the viscoelastic material is applied to the article alone. Such structures are often referred to as "free layer" dampers. However, improved damping can be obtained when the viscoelastic material is sandwiched between the article and a relatively stiff constraining layer. Such structures are often referred to as "constrained layer" dampers.
Other constructions that offer improved damping are often referred to as "damped laminates." Damped laminates are frequently used to replace sheet metal panels (e.g., sheet metal automobile body panels). The damped laminate typically contains a viscoelastic material sandwiched between two sheet metal skins. The damped laminate functions as an inherently damped structural member because the sheet metal skins are analogous to constraining layers.
A stiff viscoelastic vibration damping material could offer particular advantages in damped laminates. Damped laminates are conventionally manufactured by stamping, deep drawing or bending a large, flat sandwich construction comprising the viscoelastic material between the two sheet metal skins or constraining layers. These operations convert the flat, planar sandwich construction into a "three-dimensional" article. However, these operations also exert considerable stress on the flat sandwich construction. Sometimes these stresses are relieved by slight, involuntary shifting of the adjacent constraining layers skins relative to each other, but such movement is undesirable. A stiff viscoelastic material would better resist this movement.
The stiffness of a panel is directly proportional to the cube of the panel's thickness. Thus, replacing a single sheet metal panel with a damped laminate that incorporates two sheet metal skins, each having one-half the thickness of the original panel, yields a damped laminate that could have one-fourth the stiffness of the original panel. This reduction in stiffness may be undesirable. Incorporating a stiff viscoelastic material between the two sheet metal skins would increase the stiffness of the damped laminate.
Thus, there is considerable need for stiff vibration damping materials. Stiff vibration damping materials would be useful in damped laminates that are subsequently processed by stamping, deep drawing, or bending if the adjacent sheet metal skins were less likely to shift relative to each other. Stiff vibration damping materials could also improve the stiffness of the damped laminates. Preferably, however, any increase in stiffness will not cause a loss of damping performance. The increase in stiffness should desirably be accompanied by at least equivalent damping performance and, ideally, increased damping performance. However, a stiff viscoelastic vibration damping material can reduce vibration damping performance. It would also be advantageous if the temperature range over which good damping performance was provided could be expanded. Stiff vibration damping materials would also be useful in free layer and constrained layer dampers if they caused an overall increase in damping performance.